This invention relates to a wet type sliding apparatus, more particularly, to a wet type sliding apparatus which comprises a wet type sliding member having excellent sliding characteristics. The wet type sliding apparatus in which a lubricating oil is used at the sliding surface includes compressor, hydraulic pump, hydraulic cylinder, shock absorber, geared motor and the like.
This invention further relates to an improved wet type sliding apparatus in which a specific multilayer sliding member is used in the presence of an oil.
A multilayer sliding member in which a backing metal is coated with a sliding resin is used in a so-called dry type sliding apparatus in which, for example, a lubricating oil is not used, and various improvements have been made on a sliding resin constituting the surface layer of the sliding member in order to enhance sliding characteristics such as friction properties, wear resistance and the like, of the sliding member. Among the polyether aromatic ketones, polyetheretherketone (referred to hereinafter as PEEK) has been studied as to whether or not it can be adopted as a sliding resin for a dry type sliding member because of its excellent friction properties, wear resistance and the like. For example, Japanese Patent Application Kokai No. 63-297,457 (referred to hereinafter as Prior Art 1) discloses a sliding resin composition comprising 99 to 80% by weight of PEEK and 1 to 20% by weight of a metal fluoride as a filler and describes that a bearing having excellent wear resistance can be formed therefrom. Japanese Patent Application Kokai No. 1-108,413 (referred to hereinafter as Prior Art 2) describes that a sliding member having low friction and excellent wear resistance can be formed from a sliding resin composition comprising 30 to 98 by weight PEEK, 1 to 35% by weight of polytetrafluoroethylene (referred to hereinafter as PTFE) as a filler and 1 to 35% by weight of a metal fluoride as a filler.
In Prior Art 1 and Prior Art 2, the application of PEEK to a sliding member to be used in the dry type sliding apparatus is discussed, and it is described that a sliding member consisting of 100% by weight of PEEK has a large friction coefficient, and hence, PEEK cannot be used alone as a sliding member. This is stated on page 1, the lower right column, line 11 to page 2, the upper left column, line 7 of Prior Art 1 and also as Comparative Example 6 in Table 1 of Prior Art 1, and it is stated there that a sliding member consisting of 100% by weight of PEEK is inferior in friction coefficient and wear resistance and hence required to contain various solid fillers in addition to the PEEK.
However, in the field of a wet type sliding apparatus in which a sliding member is used in the presence of a lubricating oil, for example, a compressor or the like, there has recently become required a sliding member (bearing) capable of reducing the consumed electric power and minimizing noise, and particularly as to the noise, even a frictional noise as generated when a shaft is rotated in a bearing has become a problem.
The present inventors have made extensive research to solve the above problems and, as a result, have surprisingly found that when a sliding resin consisting essentially of PEEK is used alone as a sliding resin for a sliding member in the wet type sliding apparatus, the results obtained are quite different from those obtained under the dry type sliding conditions. This invention is based on the above knowledge.